This is a fun Christmas piece for SAB choir and keyboard that's easy to put together.
An effective contrast between baritone and treble voices can be set up on pages 4 and 5 if baritones sing the ostinato, “Gloria in excelsis Deo...” non legato with quiet rhythmic energy while altos and sopranos sing their part, “Et in terra pax...” legato and rather full. Add percussion for increased rhythmic interest.
Glory to God in the highest. And on earth, peace to all those of good will.